Abstract

Optical emission spectroscopy (OES) and spectroscopic temperature determination were carried out to study ${\mathrm{C}}_2{\mathrm{H}}_4/{\mathrm{C}}_2{\mathrm{H}}_2/{\mathrm{O}}_2$ flames used for diamond deposition with and without an excitation by a wavelength-tunable ${\mathrm{CO}}_2$ laser. Strong emissions from ${\mathrm{C}}_2$ and CH radicals were observed in the visible range in all the acquired OES spectra. When the flames were irradiated by using a continuous-wave (CW) ${\mathrm{CO}}_2$ laser at a wavelength of $10.591\mathrm{\mu m}$, the emission intensities of the ${\mathrm{C}}_2$ and CH radicals in the flames increased owing to the laser excitation. The ${\mathrm{CO}}_2$ laser was also tuned to a wavelength of $10.532\mathrm{\mu m}$ to precisely match the resonant frequency of the ${\mathrm{CH}}_2$-wagging vibrational mode of the ${\mathrm{C}}_2{\mathrm{H}}_4$ molecules. OES spectroscopy of the ${\mathrm{C}}_2$ and CH radicals were performed at different laser powers. The rotational temperatures of CH radicals in the flames were determined by analyzing the spectra of the R branch of the $A^2\mathrm{\Delta }\to X^2\mathrm{\Pi }$ $(0,0)$ electronic transition near $430\mathrm{nm}$. The deposited diamond thin-films were characterized by scanning electron microscopy, stylus profilometry, and Raman spectroscopy. The deposition mechanism with and without the ${\mathrm{CO}}_2$ laser excitation was discussed based on the OES spectral results.

© 2010 Optical Society of America

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